The present invention relates to self-induction-type position detector devices which include a coil to be excited by an A.C. signal and a magnetic or electrically-conductive member movable relative to the coil and which are suitable for detection of a linear or rotational position. More particularly, the present invention relates to an improved self-induction-type position detector device which, in response to a position of an object of detection (i.e., an object to be detected), can generate A.C. output signals presenting amplitude function characteristics of a plurality of phases using only a primary coil to be excited by a single-phase A.C. output signal.
There have ben known induction-type linear position detector devices which are commonly called xe2x80x9cLVDTsxe2x80x9d. In two-wire-type LDVTs including one primary coil and one secondary coil, an induction coupling between the primary coil and the secondary coils varies in accordance with an amount of entry, into a coil section, of a movable section made of a magnetic substance, so that an inductive output signal of a voltage level corresponding to the induction coupling variation is produced in the secondary coil. Further, three-wire-type LDVTs are constructed as a differential transformer including one primary coil and two secondary coils connected in series in opposite phases, where an induction coupling between the primary coil and the secondary coils varies in a balanced manner in accordance with an amount of entry, into one of the two coils of the opposite phases, of a movable section made of a magnetic substance having a predetermined length, so that inductive output signals of voltage levels corresponding to the induction coupling variation are produced in the secondary coils. In such three-wire-type LDVTS, output signals of sine and cosine characteristics corresponding to a position of the movable section are generated by performing analog addition or subtraction on the output signals from the secondary coils, and these output signals of sine and cosine characteristics are then processed via an R-D converter to thereby generate digital data indicative of a detected current position of the movable section. Other type of position detector device have also been known (e.g., from Japanese Patent Laid-open Publication No. SHO-53-102070 and U.S. Pat. No. 4,112,365 corresponding thereto), which include only an exciting coil and where a variation in the self-inductance of the exciting coil responding to a movement of a movable magnetic core is detected by measuring an amount of phase shift through an R-L circuit.
However, because the conventionally-known LVDTs require both of the primary and secondary coils, the necessary number of component parts would increase, which unavoidably results in significant limits to reduction in the manufacturing cost and size of the devices. In addition, an available phase angle range in the output signals of sine and cosine characteristics corresponding to a current position of the movable section is relatively narrow, such as about 45xc2x0 in the two-wire-type LVDTs or about 90xc2x0 in the three-wire-type LVDTs, so that the detectable phase angle range can not be expanded satisfactorily in the conventionally-known LVDTs. Further, because the conventional three-wire-type LVDTs can only detect such positions displaced leftward and rightward from a predetermined reference point where the movable section is located centrally along the length the coil section, they provide a very poor convenience of use.
With the conventionally-known position detector devices of the type which measures the self-inductance of the exciting coil, on the other hand, it is possible to reduce the necessary number of coils, but the phase shift amount responding to the displacement of the object to be detected can be detected only within an extremely narrow range, which, in effect, would make it very difficult to measure the phase shift amount. Also, these known position detector devices provide a very poor detecting resolution and thus are not suitable for practical use. In addition, because the phase shift amount varies as the impedance of the coil changes in response to a change in ambient temperature, the position detector devices could not properly compensate or adjust their temperature characteristics.
Induction-type rotational position detector devices of the type which produces two-phase outputs (i.e., outputs of sine and cosine phases) in response to a single-phase exciting input are commonly known as xe2x80x9cresolversxe2x80x9d, and induction-type rotational position detector devices of the type which produces three-phase outputs (i.e., outputs of three phases shifted from each other by 120xc2x0) in response to a single-phase exciting input are commonly known as xe2x80x9csynchrosxe2x80x9d. In the resolvers in the most traditional form, a stator includes two-pole (sine and cosine poles) secondary windings that intersect each other at a 90xc2x0 mechanical angle, and a rotor includes a primary winding. The resolvers of this type are not satisfactory in that they need a brush to electrically contact the primary winding of the rotor. There have also been known brush-less resolvers that require no such brush; that is, these brush-less resolvers include, in the rotor, a rotary transformer in place of the brush. However, because of the provision of the rotary transformer in the rotor, it is difficult to reduce the overall size of the devices and thus there are limitations to the downsizing of the brush-less resolvers. Further, the provision of the rotary transformer increases the number of the component parts, which also leads to an unavoidable increase in the manufacturing cost.
Also known in the art are rotational position detector devices of the non-contact/variable-reluctance type (known in the past by the tradename xe2x80x9cmicrosynxe2x80x9d), where a stator includes primary and secondary windings disposed on a plurality of projecting poles and a rotor is formed of a magnetic body having a predetermined shape (such as an eccentric circular shape, an oval shape or a shape having a projection). In these rotational position detector devices (rotary-type position detector devices), a reluctance variation responding to a rotational position of the object to be detected is produced on the basis of variations in gaps between the stator""s projecting poles and the rotor""s magnetic body that occur in response to a changing rotational position of the object to be detected, so that an output signal corresponding to the reluctance variation is provided. Further, similar reluctance-based rotational position detector devices are also disclosed, for example, in U.S. Pat. No. 4,754,220, Japanese Patent Laid-open Publication Nos. SHO-55-46862, SHO-55-70406 and SHO-59-28603. As position detection techniques based on the detector output signal, there have been known both a phase-based scheme in which position detecting data corresponds to an electrical phase angle of the output signal and a voltage-based scheme in which position detecting data corresponds to a voltage level of the output signal. In the case where the phase-based scheme is employed, the individual primary windings disposed at different mechanical angles are excited by phase-shifted inputs, such as two-phase or three-phase exciting inputs, so as to generate a single-phase output signal having a different electrical angle corresponding to a current rotational position. Further, in the case where the voltage-based scheme is employed, the relationship between the primary and secondary windings is reversed from that in the phase-based scheme, and plural-phase outputs are produced in response to a single-phase exciting input in the same manner as in the resolvers.
Typically, the rotational position detector devices, such as the resolvers, which produce plural-phase outputs in response to a single-phase, are arranged to produce two-phase outputs, namely, sine-phase and cosine-phase outputs. To this end, in the conventional resolver-style rotational position detector devices of the non-contact/variable-reluctance type, the stator has at least four poles that are spaced apart from each other by a mechanical angle of 90xc2x0; specifically, if the first pole is set to a sine phase, the second pole 90xc2x0 apart from the first pole is set to a cosine phase, the third pole 90xc2x0 apart from the second pole is set to a minus sine phase and the fourth pole 90xc2x0 apart from the third pole is set to a minus cosine phase. In such a case, to bring about a reluctance variation, corresponding to a rotation of the object to be detected, in each of the stator poles, the rotor is formed of a magnetic or electrically-conductive substance into an eccentric circular shape, oval shape or cyclic shape such as a gear shape. Primary and secondary windings are disposed on each of the stator poles so that a reluctance in a magnetic circuit passing through the stator pole is changed in response to a variation in a gap between the stator pole and the rotator. The reluctance change causes a degree of magnetic coupling between the primary and secondary coils on each of the stator poles to vary in correspondence with a rotational position of the object to be detected, and thus an output signal corresponding to the rotational position is induced in each of the secondary winding, with the result that a peak amplitude characteristic in the output signal from each of the stator poles presents a cyclic function characteristic.
However, because the above-discussed resolver-style rotational position detector devices of the non-contact/variable-reluctance type are based on primary-secondary induction by the provision of the primary and secondary coils, a great number of coils are required, which would unavoidably result in limits to reduction in the manufacturing cost and overall size of the devices. Further, with the arrangement that the plurality of stator poles are disposed at equal intervals along the entire range of one full rotation, the conventional rotational position detector devices would present the problem that places and space to which the devices are applicable are limited to a considerable degree. Besides, even where two-phase (sine-phase and cosine-phase) outputs are to be produced from the conventional rotational position detector devices, the stator can not be constructed as a simple two-pole structure and always has to be constructed as a more complicated four-pole structure, which would also impose limitations to reduction in the overall size of the stator.
It is therefore an object of the present invention to provide an improved position detector device which is very compact in size and very simple in structure. It is another object of the present invention to provide an improved position detector device which achieves a significant increase in its available phase angle range, can accurately detect even microscopic displacement of an object to be detected with high resolution and also can readily compensate its temperature characteristics in an appropriate manner.
In order to accomplish the above-mentioned object, the present invention provides a position detector device which comprises: a coil section including at least one coil to be excited by an A.C. signal; a magnetism-responsive member movable relative to said coil section, wherein relative positions between said magnetism-responsive member and said coil section vary in response to displacement of an object to be detected and impedance of said coil is caused to vary in response to a variation in the relative positions in such a manner that a voltage produced in said coil is caused to vary in response to a variation in the impedance of said coil during the variation in the relative positions within a predetermined range; a reference-voltage generation circuit adapted to generate at least one predetermined reference voltage in the form of an A.C. signal; and an arithmetic operation circuit coupled to said coil and reference-voltage generation circuit, said arithmetic operation circuit adapted to perform an arithmetic operation between said voltage produced in said coil and said predetermined reference voltage, so as to generate at least two A.C. output signals having predetermined cyclic amplitude functions as amplitude coefficients, the cyclic amplitude functions of the two A.C. output signals being different, in their cyclic characteristics, from each other by a predetermined phase.
Typically, the magnetism-responsive member includes at least one of a magnetic substance and an electrically-conductive substance. In the case where the magnetism-responsive member is made of a magnetic substance, the inductance and electrical impedance of the coil increases and the voltage produced in the coil, i.e., a voltage between two terminals (i.e., xe2x80x9cbetween-terminal voltagexe2x80x9d) of the coil, increases as the magnetism-responsive member moves closer to the coil, i.e., as the degree of proximity of the magnetism-responsive member to the coil increases. Conversely, as the magnetism-responsive member moves away from the coil, i.e., as the degree of proximity of the magnetism-responsive member to the coil decreases, the inductance and electrical impedance of the coil decreases and the voltage produced in the coil, i.e., xe2x80x9cbetween-terminal voltagexe2x80x9d of the coil, decreases. Thus, in response to displacement (changing position) of the object to be detected, the between-terminal voltage of the coil increases or decreases as the relative position of the magnetism-responsive member to the coil varies within a predetermined range.
Typically, a progressive variation curve of the between-terminal voltage of the coil, presented during the movement of the magnetism-responsive member relative to the coil, can be likened to a functional value variation within a 0xc2x0-90xc2x0 range of a sine function. If an A.C. signal component is represented by xe2x80x9csin xcfx89txe2x80x9d and an amplitude coefficient level of the output voltage Vx of the coil obtained in correspondence with the start point of an appropriate detection section in the progressive variation curve presented by the between-terminal voltage of the coil is represented by xe2x80x9cPaxe2x80x9d, the output voltage Vx from the coil corresponding to the start point of the detection section can be represented by xe2x80x9cPa sin xcfx89txe2x80x9d. Similarly, if an amplitude coefficient level of the output voltage Vx of the coil obtained in correspondence with the end point of the above-mentioned detection section in the progressive variation curve is represented by xe2x80x9cPbxe2x80x9d, then the coil output voltage corresponding to the end point of the detection section can be represented by xe2x80x9cPb sin xcfx89txe2x80x9d. Further, if an A.C. voltage having the same value as the value Pa sin xcfx89t of the coil output voltage Vx corresponding to the start point of the detection section is set as a reference value Va and the amplitude coefficient of the coil output voltage Vx is represented by A(x), subtracting the first reference voltage Va from the coil output voltage Vx gives the following mathematical expression:
Vxxe2x88x92Va=A(x)sin xcfx89txe2x88x92Pa sin xcfx89t={A(x)xe2x88x92Pa}sin xcfx89txe2x80x83xe2x80x83Expression(1)
Because A(x) equals Pa at the start point of the detection section, the amplitude coefficient xe2x80x9cA(x)xe2x88x92Paxe2x80x9d, which is the result of these arithmetic operations, becomes xe2x80x9c0xe2x80x9d. On the other hand, at the end point of the detection section, A(x) equals Pb, so that the amplitude coefficient xe2x80x9cA(x)xe2x88x92Paxe2x80x9d, which is the result of these arithmetic operations, equals xe2x80x9cPbxe2x88x92Paxe2x80x9d. Thus, the xe2x80x9cA(x)xe2x88x92Paxe2x80x9d, the result of these arithmetic operations, presents a function characteristic increasing progressively from xe2x80x9c0xe2x80x9d to xe2x80x9cPbxe2x88x92Paxe2x80x9d. If the maximum value xe2x80x9cPbxe2x88x92Paxe2x80x9d is regarded equivalently as xe2x80x9c1xe2x80x9d, then the amplitude coefficient xe2x80x9cA(x)xe2x88x92Paxe2x80x9d of the A.C. signal based on Expression (1) above varies from xe2x80x9c0xe2x80x9d to xe2x80x9c1xe2x80x9d within the detection section, and the function characteristic of the amplitude coefficient can be likened to a characteristic of a first quadrant (i.e., a 0xc2x0-90xc2x0 range) in a sine function. Therefore, the amplitude coefficient xe2x80x9cA(x)xe2x88x92Paxe2x80x9d of the A.C. signal based on the above mathematical expression can be expressed equivalently as sin xcex8 (approximately, 0xc2x0xe2x89xa6xcex8xe2x89xa690xc2x0).
In a preferred implementation of the position detector device, the coil section includes a single coil, and the reference-voltage generation circuit generates first and second reference voltages. The arithmetic operation circuit performs predetermined first and second arithmetic operations using a voltage taken out from the single coil and the first and second reference voltages, to thereby generate a first A.C. output signal having a first amplitude function as an amplitude coefficient and a second A.C. output signal having a second amplitude function as an amplitude coefficient. In this case, the position detector device requires only one coil and thus can be as simple as possible in structure. Further, using the voltage Va as the above-mentioned first reference voltage, the above-mentioned first amplitude function can have a characteristic corresponding generally to the first quadrant (i.e., the 0xc2x0-90xc2x0 range) in the sine function.
If an A.C. voltage having the same value as the value Pb sin xcfx89t of the coil output voltage Vx corresponding to the end point of the detection section is set as a second reference value Vb, subtracting the second reference voltage Vb from the coil output voltage Vx gives the following mathematical expression:
Vbxe2x88x92Vx=Pb sin xcfx89txe2x88x92A(x)sin xcfx89t={Pbxe2x88x92A(x)}sin xcfx89txe2x80x83xe2x80x83Expression (2)
Because A(x) equals Pa at the start point of the detection section, the amplitude coefficient xe2x80x9cPbxe2x88x92A(x)xe2x80x9d, which is the result of these arithmetic operations, equals xe2x80x9cPbxe2x88x92Paxe2x80x9d. On the other hand, at the end point of the detection section, A(x) equals Pb, so that the amplitude coefficient xe2x80x9cPbxe2x88x92A(x)xe2x80x9d, which is the result of these arithmetic operations, becomes xe2x80x9c0xe2x80x9d. Thus, the xe2x80x9cPbxe2x88x92A(x)xe2x80x9d, the result of these arithmetic operations, presents a function characteristic decreasing progressively from xe2x80x9cPbxe2x88x92Paxe2x80x9d to xe2x80x9c0xe2x80x9d. If the maximum value xe2x80x9cPbxe2x88x92Paxe2x80x9d is regarded equivalently as xe2x80x9c1xe2x80x9d, then the amplitude coefficient xe2x80x9cPbxe2x88x92A(x)xe2x80x9d of the A.C. signal based on Expression (2) above varies from xe2x80x9c1xe2x80x9d to xe2x80x9c0xe2x80x9d within the detection section, and the function characteristic of the amplitude coefficient can be likened to a characteristic of a first quadrant (i.e., a 0xc2x0-90xc2x0 range) in a cosine function. Therefore, the amplitude coefficient xe2x80x9cPbxe2x88x92A(x)xe2x80x9d of the A.C. signal based on Expression (2) can be expressed equivalently as cos xcex8 (approximately, 0xc2x0xe2x89xa6xcex8xe2x89xa690xc2x0). The subtraction in Expression (2) may be replaced by xe2x80x9cVxxe2x88x92Vbxe2x80x9d.
In the above-mentioned manner, by only using a combination of one coil and two reference voltages, the present invention can readily produce two A.C. output signals presenting amplitudes of sine and cosine function characteristics, in response to a current position of the object to be detected. For example, if the position of the object to be detected is represented by an angle xcex8, then the A.C. output signal presenting an amplitude of a sine function characteristic can be expressed by sin xcex8 sin xcfx89t while the A.C. output signal presenting an amplitude of a cosine function characteristic can be expressed by cos xcex8 sin xcfx89t. These output signals are just similar in form to the outputs from the known position detector devices commonly called xe2x80x9cresolversxe2x80x9d, which are therefore extremely useful in various applications. In some application, the inventive position detector device may further comprise an amplitude-to-phase converter section that receives the plurality of A.C. output signals generated via the above-mentioned arithmetic operation circuit, then detects, from a correlation between the amplitude values of the A.C. output signals, a specific phase value in the sine and cosine functions defining the amplitude values, and then generates position detecting data indicative of a current position of the object to be detected. Note that because the sine and cosine functions each present a characteristic within a range of substantially one quadrant (90xc2x0), every position over a detectable position range can be detected in terms of a phase angle within the substantially-90xc2x0 range.
In this case, variably setting the levels Pa and Pb of the reference voltages Va and Vb would result in variably setting the detectable position range of the device. If the levels Pa and Pb of the reference voltages Va and Vb are set to be greatly different from each other, then the detectable position range will be widened accordingly, while if the levels Pa and Pb of the reference voltages Va and Vb are set to be only slightly different from each other, then the detectable position range will be narrowed. Because any position within the detectable position range can always be detected in terms of a phase angle xcex8 within the substantially-90xc2x0 range irrespective of a change in the detectable position range, the detecting resolution of the inventive position detection can be variably set by just variably setting the levels of the reference voltages Va and Vb. This means that the position detection can be made with a super-high resolution even where very minute or microscopic displacement of the object is to be detected.
In another preferred embodiment, the coil section includes two coils, relative positions of the two coils relative to the magnetism-responsive member being caused to vary with opposite characteristics in response to the displacement of the object to be detected, in response to which respective impedance of the coils varies with opposite characteristics. In this case, the reference-voltage generation circuit generates a single reference voltage, and the arithmetic operation circuit performs predetermined first and second arithmetic operations using voltages taken out from the coils and the reference voltage, to thereby generate a first A.C. output signal having a first amplitude function as an amplitude coefficient and a second A.C. output signal having a second amplitude function as an amplitude coefficient.
Similarly to the above-mentioned, a progressively increasing variation curve of the between-terminal voltage of the first coil, presented during a variation of the relative position of the magnetism-responsive member within a predetermined range, can be likened to a functional value variation in a 0xc2x0-90xc2x0 range of a sine function. Namely, the output voltage Vx from the coil corresponding to the start point of an appropriate detection section can be represented by Pa sin xcfx89t, which corresponds to a minimum voltage value. The start point of the detection section can be set by the reference voltage Va. Performing arithmetic operations similar to Equation (1) above using the reference voltage Va (=Pa sin xcfx89t) gives
Vxxe2x88x92Va={A(x)xe2x88x92Pa}sin xcfx89t
As in the above-mentioned case, the function characteristic of the amplitude coefficient xe2x80x9cA(x)xe2x88x92Paxe2x80x9d can be likened to a characteristic of the first quadrant (i.e., the 0xc2x0-90xc2x0 range) in a sine function, namely, it can be expressed equivalently as sin xcex8 (approximately, 0xc2x0xe2x89xa6xcex8xe2x89xa690xc2x0).
On the other hand, the second coil in the coil section presents a progressively decreasing variation curve opposite to the curve of the first coil. The output voltage Vy from the second coil corresponding to the start point of the detection section can be represented provisionally by xe2x80x9cPaxe2x80x2 sin xcfx89txe2x80x9d, which corresponds to a maximum voltage value. Subtracting the reference voltage Va from the second coil output voltage Vy gives the following mathematical expression where the amplitude coefficient of the output voltage Vy is represented by A(y):
Vyxe2x88x92Va=A(y)sin xcfx89txe2x88x92Pa sin xcfx89t={A(y)xe2x88x92Pa}sin xcfx89txe2x80x83xe2x80x83Expression (3)
Because A(y) equals Paxe2x80x2 at the start point of the detection section, the amplitude coefficient xe2x80x9cA(y)xe2x88x92Paxe2x80x9d, which is the result of the arithmetic operations, equals xe2x80x9cPaxe2x80x2xe2x88x92Paxe2x80x9d representing xe2x80x9cmaximum valuexe2x88x92minimum valuexe2x80x9d, which therefore becomes a maximum value that can be regarded equivalently as xe2x80x9c1xe2x80x9d. At the end point of the detection section, on the other hand, A(y) equals Pa, so that the amplitude coefficient xe2x80x9cA(y)xe2x88x92Paxe2x80x9d, the result of the above arithmetic operations, becomes xe2x80x9c0xe2x80x9d. Thus, the amplitude coefficient xe2x80x9cA(y)xe2x88x92Paxe2x80x9d presents a function characteristic progressively decreasing from the maximum value xe2x80x9cPaxe2x80x2xe2x88x92Paxe2x80x9d (namely, xe2x80x9c1xe2x80x9d) to xe2x80x9c0xe2x80x9d within the range of the detection section. This function characteristic of the amplitude coefficient can be likened to a characteristic of the first quadrant (i.e., the 0xc2x0-90xc2x0 region) in the cosine function. Therefore, the amplitude coefficient xe2x80x9cA(y)xe2x88x92Paxe2x80x9d of the A.C. output signal based on Expression (3) above can be expressed equivalently as cos xcex8 (approximately, 0xc2x0xe2x89xa6xcex8xe2x89xa690xc2x0).
Thus, in the case where a combination of two coils and a single reference voltages is employed as above, the present invention can readily produce two A.C. output signals presenting amplitudes of sine and cosine function characteristics (sin xcex8 sin xcfx89t and cos xcex8 sin xcfx89t), in response to a current position of the object to be detected. In this case too, the sine and cosine functions each present a characteristic within a range of substantially one quadrant (90xc2x0), so that every position over a detectable position range can be detected in terms of a phase angle within the substantially-90xc2x0 range. Further, by just variably setting the level of the reference voltage Va, the detectable position range can be variably set and the detecting resolution of the device can be adjusted as desired, similarly to the above-mentioned.
Thus, according to the present invention, there can provide an improved position detector device which is very compact in size and very simple in structure, because it requires only a primary coil (or coils) with no need for a secondary coil. Further, using a combination of one coil and two reference voltages or a combination of two coils and one reference voltage, the present invention can readily produce a plurality of A.C. output signals presenting amplitudes of predetermined cyclic function characteristics (e.g., two A.C. output signals presenting amplitudes of sine and cosine function characteristics), in response to a current linear position of the object to be detected, and also can provide at least about one quadrant (90xc2x0) as an available phase angle range. Thus, even with a reduced number of coils, the present invention is capable of effective position detection over a relatively wide phase angle range and also achieves a highly enhanced detecting resolution. Besides, even for very minute or microscopic displacement of the object to be detected, the present invention allows a position of the object to be detected with a high resolution. Furthermore, by employing a circuit (e.g., a coil) presenting temperature characteristics similar to those of the detecting coils as the reference-voltage generation circuit, predetermined subtractive arithmetic operations in arithmetic operation circuitry can automatically compensate the temperature drift characteristics in an appropriate manner, thereby providing for high-accuracy position detection without influences of a temperature change. Further, to construct the reference-voltage generation circuit, a resistor or other suitable element may be used in place of the coils. Furthermore, the numbers of the coil and reference voltage may be greater than one or two, in which case the available phase angle range may be expanded to be greater than about one quadrant (90xc2x0).
The position detector device of the present invention can also be constructed as a rotary-type position detector device. If the amplitude coefficient component produced by an incremental (increasing) or decremental (decreasing) variation in the between-terminal voltage of a coil, corresponding to a rotational displacement of the object to be detected is represented by a function A(xcex8) with a rotational angle e as a variable, the between-terminal voltage of the coil can be expressed by A(xcex8)sin xcfx89t. In this case, the amplitude coefficient component A(xcex8) takes only a positive value although it increases or decreases in accordance with the rotational displacement of the object to be detected. Assuming that the incremental/decremental variation curve of the amplitude coefficient component A(xcex8) presents a characteristic approximate to that of a sine curve and if its peak value is denoted by P, the amplitude coefficient component A(xcex8) can be expressed typically by an equation of xe2x80x9cA(xcex8)=Po+P sin xcex8xe2x80x9d, where Poxe2x89xa7P. Namely, the amplitude coefficient component A(xcex8) presents such a characteristic that is obtainable by offsetting the value of P sin xcex8 with the offset value Po.
The rotary-type position detector device of the present invention is characterized by: generating a predetermined reference voltage; taking out a voltage between terminals of a coil; and performing an arithmetic operation between the predetermined reference voltage and the taken-out between-terminal voltage of the coil, so as to generate an A.C. output signal having a predetermined cyclic amplitude function as an amplitude coefficient. If the predetermined reference voltage is represented by Po sin xcfx89t, subtracting the reference voltage Po sin xcfx89t from the between-terminal voltage of the coil A(xcex8)sin xcfx89t gives
A(xcex8)sin xcfx89txe2x88x92Po sin xcfx89t=(Po+Po sin xcex8)sin xcfx89txe2x88x92Po sin xcfx89t=Po sin xcex8 sin xcfx89t 
By performing arithmetic operations between the output signal from the single coil and the reference voltage, there can be generated an A.C. output signal having an amplitude coefficient component of a real sine function sine (or real cosine function) swinging in the positive and negative directions. Such inventive arrangements can greatly simplify the necessary coil structure. Further, the present invention can provide an improved rotary-type position detector device which is event more compact in size and even simpler in structure, because it requires only a primary coil with no need for a secondary coil.
In one embodiment of the inventive rotary-type position detector device, the coil section includes two coils positioned to be apart from each other by a predetermined angle along a direction of variation of relative rotational positions between the coils and the magnetism-responsive member, and the reference-voltage generation circuit generates a reference voltage (e.g., Po sin xcfx89t) corresponding to a center point of variation in a voltage between terminals of each of the two coils. The arithmetic operation circuit subtracts the reference voltage from the voltage between the terminals of a first one of the two coils to cancel out a voltage offset corresponding to the reference voltage and thereby generates a first A.C. output signal (e.g., sin xcex8 sin xcfx89t) having, as an amplitude coefficient, a first cyclic amplitude function swinging about the center point of variation in positive and negative directions. The arithmetic operation circuit also subtracts the reference voltage from the voltage between the terminals of a second one of the two coils to cancel out a voltage offset corresponding to the reference voltage and thereby generates a second A.C. output signal (e.g., cos xcex8 sin xcfx89t) having, as an amplitude coefficient, a second cyclic amplitude function swinging about the center point of variation in the positive and negative directions. In this case, by providing only two coils, there can be generated a sine-phase output signal (sin xcex8 sin xcfx89t) and a cosine-phase output signal (cos xcex8 sin xcfx89t) similar to those produced by the known resolvers.
In another embodiment of the inventive rotary-type position detector device, the arithmetic operation circuit performs predetermined first and second arithmetic operations using the voltage between the terminals of one of the coils and the reference voltage, to thereby generate a first A.C. output signal having a first amplitude function as its amplitude coefficient and a second A.C. output signal having a second amplitude function as its amplitude coefficient. In this case, respecting a rotational displacement of the object within a predetermined limited range of mechanical rotational angles, position detecting data can be obtained on a predetermined limited phase detecting scale (i.e., a 90xc2x0 range) rather than a full 360xc2x0 phase detecting scale, as will be later described more fully. Despite the predetermined limited phase detecting scale, there can be generated a sine-phase output signal (sin xcex8 sin xcfx89t) and cosine-phase output signal (cos xcex8 sin xcfx89t) similar to those produced by the known resolvers, using only one coil.
In another implementation of the inventive rotary-type position detector device, the coil section may be provided in a predetermined limited angular range less than one full rotation range of the object to be detected so that the detector device can be suitably used to detect a rotational position within the predetermined limited angular range. Such a coil section extending only over a limited or biased angular range will be useful particularly in a situation where the rotary-type position detector device of the present invention is to be installed in a previously installed machine or apparatus. Namely, where some large obstacle is already present within the predetermined rotating angle range of an rotation shaft, which is the object to be detected, and it is impossible to install the stator coil section over a range corresponding to the full rotation of the rotation shaft, the coil section extending only over the limited angular range in the embodiment can be readily installed in an obstacle-free angular range, and thus can be very useful.
A rotary-type position detector device according to another aspect of the present invention comprises: a coil section including at least two pairs of coils to be excited by an A.C. signal, the coils in each of the pairs being positioned to be apart from each other by a distance corresponding to a predetermined rotational angle; a magnetism-responsive member rotationally movable relative to said coil section, wherein relative rotational positions between said magnetism-responsive member and said coil section vary in response to rotational displacement of an object to be detected and impedance of each of said coils is caused to vary in response to a variation in the relative rotational positions in such a manner that a voltage produced in each of said coils is caused to vary in response to a variation in the impedance of said coil during the variation in the relative rotational positions within a predetermined rotational angle range, the voltages produced in the respective coils in each of the pairs presenting differential characteristics; and a circuit coupled to said coil section, said circuit adapted to generate, for each of said two pairs of coils, an A.C. output signal having a predetermined cyclic amplitude function as an amplitude coefficient, by taking out a difference in the voltages produced in said respective coils, the cyclic amplitude functions of the A.C. output signals generated for said two pairs of coils being different in their cyclic characteristics by a predetermined phase.
If one of the coil pairs in the thus-constructed rotary-type position detector device is be of a sine phase and if one of the coils in the pair presents a characteristic of (Po+Po sin xcex8)sin xcfx89t, then the other coil in the pair presents a characteristic of (Poxe2x88x92Po sin xcex8)sin xcfx89t, because the incremental/decremental variations in the produced voltages, i.e., between-terminal voltages, of the coils in that pair present differential characteristics. Thus, taking out a difference between the two characteristics gives
(Po+P sin xcex8)sin xcfx89txe2x88x92{(Poxe2x88x92P sin xcex8))sin xcfx89t}=2P sin xcex8 sin xcfx89t
Further, If the other coil pair in this inventive rotary-type position detector device is be of a cosine phase, the incremental/decremental variations in the between-terminal voltages of the coils in that pair present differential characteristics as follows. Namely, taking out a difference between the two characteristics gives
(Po+P cos xcex8)sin xcfx89txe2x88x92{(Poxe2x88x92P cos xcex8)sin xcfx89t}=2P cos xcex8 sin xcfx89t
Such a different ial synthesis principle employed in the present invention is generally similar to the one already known in the field of the resolvers, except that the conventional-known resolvers would require both primary and secondary coils. Namely, in contrast to the conventional-known resolvers, the present invention requires only primary coils with no need for any secondary coil and thus can simplify the necessary coil structure, with the result that there can be provided an improved rotary-type position detector device significantly simplified in structure.
A position detector device according to still another aspect of the present invention comprises: a coil section including a plurality of coil segments to be excited by a predetermined A.C. signal, the coil segments being placed in series along a direction of displacement of an object to be detected; a magnetism-responsive member movable relative to said coil section, wherein relative positions between said magnetism-responsive member and said coil section vary in response to displacement of the object to be detected and impedance of each of said coil segments is caused to vary in response to a variation in the relative positions in such a manner that a voltage produced in each of said coil segments is caused to progressively increase or decrease during a movement of said magnetism-responsive member from one end to another of each of said coil segments; and an analog arithmetic operation circuit coupled to said coil section, said analog arithmetic operation circuit adapted to generate a plurality of A.C. output signals presenting amplitudes based on predetermined cyclic function characteristics corresponding to a position of the object to be detected, by taking out voltages of said coil segments and performing addition and/or subtraction on the taken-out voltages, the cyclic function characteristics defining the amplitudes of the plurality of A.C. output signals comprising cyclic functions of a same character that are different from each other by a predetermined phase.
Typically, the magnetism-responsive member includes at least one of a magnetic substance and an electrically-conductive substance. In the case where the magnetism-responsive member is made of a magnetic substance, as the magnetism-responsive member moves closer to any one of the coil segments, i.e., as the degree of proximity of the magnetism-responsive member to the coil segments increases, the self-inductance of the coil segment increases and the voltage produced in the coil segment (i.e., a between-terminal voltage of the coil segment) progressively increases during a movement of the tip of the magnetism-responsive member from one end to the other of the coil segment. By the sequential placement of the plurality of coil segments along the direction of displacement of the object to be detected, a progressive increase (or progressive decrease) occurs sequentially in the between-terminal voltages of the coil segments as the magnetism-responsive member moves relative to these coil segments in response to the displacement of the object to be detected. Thus, by combining and using the progressive increases (or progressive decreases) in the between-terminal voltages of the individual coil segments while regarding them as variations in partial phase ranges of predetermined cyclic functions, the present invention can generate a plurality of A.C. output signals presenting amplitudes based on predetermined cyclic function characteristics corresponding to a current position of the object to be detected. Namely, the plurality of A.C. output signals presenting amplitudes based on predetermined cyclic function characteristics, corresponding to a position of the object to be detected, can be generated by taking out the between-terminal voltages of the coil segments and performing addition and/or subtraction on the taken-out voltages.
Typically, a progressively-increasing variation curve of the between-terminal voltage of any one of the coil segments, which takes place during the movement of the magnetism-responsive member from the coil""s one end to the other, can be likened, for example, to a functional value variation over a 0xc2x0-90xc2x0 range of a sine function. Further, this progressively-increasing variation curve can be converted into a variation curve progressively decreasing from a predetermined level, by inverting the amplitudes of the voltages and performing a voltage shift operation to add a predetermined offset level to the inverted amplitudes. Such a progressively-decreasing variation curve of the between-terminal voltage can be likened, for example, to a functional value variation over a 90xc2x0-180xc2x0 range of a sine function. Thus, the progressively-increasing variations of the between-terminal voltage, sequentially occurring, for example, in a series of four coil segments, can be likened to function value variations in the 0xc2x0-90xc2x0 range, 90xc2x0-180xc2x0 range, 180xc2x0-270xc2x0 range and 270xc2x0-360xc2x0 range, respectively. Sloping direction and voltage-shifting offset level in each of these ranges can be controlled as appropriate through suitable analog arithmetic operations. Thus, the present invention can generate a first A.C. output signals presenting amplitudes based on the sine function characteristic corresponding to a position of the object to be detected, as well as a second A.C. output signals presenting amplitudes based on the same-character cyclic function, i.e., the cosine function characteristic, which is shifted in phase from the sine function by 90xc2x0.
Thus, as a preferred embodiment of the present invention, there can be generated two A.C. output signals presenting amplitudes based on the sine and cosine function characteristics corresponding to a current position of the object to be detected. Generally, the A.C. output signals having amplitudes based on the sine function characteristic can be represented by sinesinot, while the A.C. output signals having amplitudes based on the cosine function characteristic can be represented by cos xcex8 sin xcfx89t. These output signals are just similar in form to the outputs from the known position detector devices commonly called xe2x80x9cresolversxe2x80x9d, which are therefore extremely useful in various applications. In some application, the inventive position detector device may further comprise an amplitude-to-phase converter section that receives two A.C. output signals generated via the above-mentioned analog arithmetic operation circuit, then detects, from a correlation between the amplitude values of the A.C. output signals, a specific phase value in the sine and cosine functions defining the amplitude values, and then generates position detecting data indicative of a current position of the object to be detected.
Thus, according to the present invention, there can be provided an improved position detector device which is very compact in size and very simple in structure, because it requires only a primary coil with no need for any secondary coil. In addition, with the arrangement that a plurality of coil segments are placed in series along the direction of displacement of the object to be detected so that a progressive increase (or progressive decrease) occurs sequentially in the between-terminal voltages of the coil segments as the magnetism-responsive member moves from one end to the other of any one of the coil segments, the present invention can readily produce a plurality of A.C. output signals presenting amplitudes of predetermined cyclic function characteristics (e.g., two A.C. output signals presenting amplitudes of sine and cosine function characteristics), in response to a current linear position of the object to be detected, by taking out the between-terminal voltages of the coil segments and combining the taken-out voltages after performing addition and/or subtraction thereon. Further, the present invention can provide a wider available phase angle range; for example, the invention is also cable of detecting positions over a full phase angle range of 0xc2x0-360xc2x0. Because the plurality of A.C. output signals presenting amplitudes of predetermined cyclic function characteristics are generated by combining the output voltages from the plurality of coil segments presenting the same temperature characteristics after addition or subtraction having been performed thereon, the present invention can automatically compensate the temperature characteristics in an appropriate manner, thereby readily providing for high-accuracy position detection without influences of a temperature change. In addition, even for very minute or microscopic displacement of the object to be detected, a current position of the object can be detected with a high resolution, by detecting, from a correlation between the amplitude values of these A.C. output signals, a phase value in the predetermined cyclic functions (e.g., sine and cosine functions) defining the amplitude values.
Note that in the case where the magnetism-responsive member is made of a non-magnetic substance of good electrical conductivity, such as copper, there occurs an eddy-current loss that causes the self-inductance of the coil to decrease and the between-terminal voltage of the coil progressively decreases as the magnetism-responsive member moves closer to the coil. In this case too, the position detector device may be constructed in the same manner as mentioned above. Also, it is important to note that the magnetism-responsive member may be of a hybrid type comprising a combination of a magnetic substance and an electrically-conductive substance. As another example, the magnetism-responsive member may include a permanent magnet and the coil section may include a magnetic core. In this case, as the permanent magnet approaches, a corresponding portion of the magnetic core in the coil section is magnetically saturated or super-saturated, so that the between-terminal voltage of the coil progressively decreases in response to the movement of the magnetism-responsive member closer to the coil. Further, dummy impedance means, namely, the reference-voltage generation circuit, may comprise a resistor or inductance means such as a coil, as noted previously; however, the dummy coil has to be positioned in such a manner that its self-inductance is not influenced by the movement of the magnetism-responsive member.